A washing machine is a home appliance for washing clothes automatically. In a typical washing machine, a motor spins a tub to agitate clothes together with water containing detergent to remove dirt from the clothes. The washing machine can be classified into several types such as a pulsator, an agitator, and a drum types.
The drum type washing machine includes a horizontally mounted drum in which clothes, as the drum is rotated, are lifted and dropped to force water and detergent solution to go through the clothes to remove dirt from the clothes. Since the clothes are lifted and dropped in the drum, the drum type washing machine damages the clothes less than the pulsator type washing machine having a vertically mounted tub. Also, the clothes are cleanly washed without tangling as like it is washed with hands. In addition, the clothes are spin dried with less wrinkles.
Meanwhile, the washing process starts upon the pressing of start button after clothes are loaded in the drum and it ends after the clothes are washed, rinsed, and spin-dried.
FIG. 1 is a motor RPM versus time graph of a spin drying of a drum type washing machine according to the related art.
Referring to FIG. 1, a spin-drying process includes a sequence of operations: an unraveling operation of tangled clothes, first to third balancing operations, first and second preliminary spin dryings, an accelerating operation, and a main spin drying.
In the unraveling operation, the drum is rotated at about 50 rpm for a specific time to disentangle the clothes. In the first to third balancing operations, the drum is rotated at about 108 rpm for a specific time to uniformly arrange the clothes throughout the inside of the drum to balance the drum.
After each of the balancing operations, the eccentricity of the drum may be measured at least one time. That is, the first preliminary spin drying is carried out according to a first eccentricity measurement, the second preliminary spin drying is carried out according to a second eccentricity measurement, and then the main spin drying is carried out according to a third eccentricity measurement.
The preliminary spin dryings may be carried out two or more times to prevent noise and overload on the motor that occur when a large amount of water is removed at once from the clothes at an initial stage of the spin-drying process. In detail the preliminary spin drying operations are carried out as follows: the drum is accelerated to 170 rpm and decelerated to 108 rpm in the first preliminary spin drying; the eccentricity of the drum is measured (second measurement) as the drum is rotated at the speed of 108 rpm; and the drum is accelerated from the speed of 108 rpm to a speed of 300 rpm and decelerated back to the speed of 108 rpm in the second preliminary spin drying. After these preliminary operations, the main spin drying is started by accelerating the drum to 600 rpm and then the drum is further accelerated until the spin drying process is completed.
During the spin-drying process, the drum is rotated by the motor. The motor drives the drum at a lower speed in a washing process and at a high speed in the spin-drying process.
However, the spin-drying process of the related art is carried out according to a fixed procedure regardless of the amount of the loaded clothes in the drum. Therefore, the preliminary spin dryings can be carried out more times and longer than really required, thereby delaying the start of the main spin drying and increasing the power consumption.